What it means
Beyond reasonable doubt is the standard of proof required to convict a person of a criminal offence in Australia. The prosecution must prove guilt to this high level; if a reasonable doubt remains, the accused must be acquitted. It is a stricter standard than the civil "balance of probabilities", reflecting the serious consequences of a criminal conviction. The standard applies to the elements of the offence the prosecution must establish.
How it's used
The jury could not be sure beyond reasonable doubt, so it returned a not-guilty verdict.